My experience is with the Trijicon, but I'd bet opinions will go both ways. I would get them installed by a pro.

+1 on the Trijicon as these are what I've used for years but I haven't heard anything bad about Meprolights.

Some may beg to differ, but I would under no circumstances change out the Glock factory barrel on any of my weapons (26, 19, 17, & 21 purchased over the last 10 years).

Not only are the factory barrels highly accurate, but they also function flawlessly. Honestly, there is not much to "fix" on a Glock in my experience with the platform though I have read about certain after market modifications causing issues.

Alot of people are saying I should upgrade the sights? If so who do I go with? Trijicon? Megpro? And can I instal them myself?

Tru glo are good sights they glow night or day. For an IWB holster the Glaco sto-n-go is an awesome holster for the money -$20. I have a ton of experience with holsters and in my opinion avoid Blackhawk if possible. Kydex is also a good option